Angela Rajek

Core Cooling by Central Venous Infusion of Ice-cold (4°C and 20°C) Fluid Isolation of Core and Peripheral Thermal Compartments

Background: Central venous infusion of cold fluid may be a useful method of inducing therapeutic hypothermia. The aim of this study was to quantify systemic heat balance and regional distribution of body heat during and after central infusion of cold fluid. Methods: The authors studied nine volunteers, each on two separate days. Anesthesia was maintained with use of isoflurane, and on each day 40 ml/kg saline was infused centrally over 30 min. On one day, the fluid was 20°C and on the other it was 4°C. By use of a tympanic membrane probe core (trunk and head) temperature and heat content were evaluated. Peripheral compartment (arm and leg) temperature and heat content were estimated with use of fourth-order regressions and integration over volume from 18 intramuscular thermocouples, nine skin temperatures, and “deep” hand and foot temperature. Oxygen consumption and cutaneous heat flux estimated systemic heat balance. Results: After 30-min infusion of 4°C or 20°C fluid, core temperature decreased 2.5 6 0.4°C and 1.4 6 0.2°C, respectively. This reduction in core temperature was 0.8°C and 0.4°C more than would be expected if the change in body heat content were distributed in proportion to body mass. Reduced core temperature resulted from three factors: (1) 10 ‐20% because cutaneous heat loss exceeded metabolic heat production; (2) 50 ‐55% from the systemic effects of the cold fluid per se; and (3) approximately 30% because the reduction in core heat content remained partially constrained to core tissues. The postinfusion period was associated with a rapid and spontaneous recovery of core temperature. This increase in core temperature was not associated with a peripheral-to-core redistribution of body heat because core temperature remained warmer than peripheral tissues even at the end of the infusion. Instead, it resulted from constraint of metabolic heat to the core thermal compartment. Conclusions: Central venous infusion of cold fluid decreases core temperature more than would be expected were the reduction in body heat content proportionately distributed. It thus appears to be an effective method of rapidly inducing therapeuBackgroundCentral venous infusion of cold fluid may be a useful method of inducing therapeutic hypothermia. The aim of this study was to quantify systemic heat balance and regional distribution of body heat during and after central infusion of cold fluid.MethodsThe authors studied nine volunteers, e

Renal Function and Outcome After Continuous Flow Left Ventricular Assist Device Implantation

BACKGROUND Renal dysfunction as a risk factor with the use of left ventricular assist devices (LVAD) is controversial. We determined the effect of renal function on outcomes after continuous flow LVAD implantation. METHODS Eighty-six patients with advanced heart failure undergoing continuous flow LVAD implantation as bridge to transplantation from November 1998 to July 2007 were retrospectively analyzed. Renal function was assessed using the Modification of Diet in Renal Disease study-derived glomerular filtration rates (GFR [mL x min(-1) x 1.73 m(-2)]). Patients were categorized into two groups based on pre-LVAD GFR: those with normal renal function (GFR > 60, n = 46), and those with renal dysfunction (GFR < 60, n = 40). RESULTS Post-LVAD survival at 1, 3, and 6 months for GFR greater than 60 was 91.3%, 79.9%, 72.6%, respectively, and for GFR less than 60, it was 92.5%, 66.5%, 47.9%, respectively (p = 0.038). Bridge-to-transplant rate was lower for GFR less than 60 than for GFR greater than 60 (40.0% versus 63.0%, p = 0.033). For GFR less than 60, GFR improved on LVAD support: implant to month 6, 41.7 +/- 11.5 to 62.7 +/- 25.0 (p = 0.021). Post-LVAD survival was improved in GFR less than 60 patients who after LVAD implantation recovered renal function to GFR greater than 60 (p < 0.001). Patients with post-LVAD renal failure had significantly lower post-LVAD survival regardless of pre-LVAD renal function (p < 0.001). CONCLUSIONS Patients with renal dysfunction have poorer outcomes after continuous flow LVAD implantation. However, renal function improves after LVAD implantation and is associated with improved survival. Our data underscore the importance of end-organ function in patient selection for LVAD therapy.

Muscle Relaxation Does Not Alter Hypnotic Level During Propofol Anesthesia

Electromyographic (EMG) activity can contaminate electroencephalographic signals. Paralysis may therefore reduce the Bispectral Index (BIS) by alleviating artifact from muscles lying near the electrodes. Paralysis may also reduce signals from muscle stretch receptors that normally contribute to arousal. We therefore tested the hypothesis that nondepolarizing neuromuscular block reduces BIS. Ten volunteers were anesthetized with propofol at a target effect site concentration of 3.8 ± 0.4 &mgr;g/mL. A mivacurium infusion was adjusted to vary the first twitch (T1) in a train-of-four to 80%, 30%, 20%, 15%, 10%, 5%, or 2% of the prerelaxant intensity. At each randomly assigned T1, we measured BIS and frontal-temporal EMG intensity. BIS averaged 95 ± 4 before induction of anesthesia, and decreased significantly to 40 ± 5 after propofol administration. However, there were no significant differences at the designated block levels. Frontal-temporal EMG intensity averaged 47 ± 3 dB before induction of anesthesia, and decreased significantly to 27 ± 1 dB after propofol administration. However, there were no significant differences at the designated block levels. These data suggest that the BIS level and EMG tone are unaltered by mivacurium administration during propofol anesthesia.

Renal Function After Implantation of Continuous Versus Pulsatile Flow Left Ventricular Assist Devices

BACKGROUND This study was designed to determine the effect of continuous vs pulsatile flow devices on renal function after left ventricular assist device (LVAD) implantation. METHODS Ninety-two patients undergoing LVAD implantation as bridge-to-transplant therapy were retrospectively analyzed. Patients receiving continuous flow devices (n = 63, 68.5%) were compared with patients receiving pulsatile flow devices (n = 29, 31.5%). Renal function was assessed by 2 calculated glomerular filtration rates (GFR) using the Modification of Diet in Renal Disease (MDRD)-derived GFR (ml/min/1.73 m(2)) and the Cockcroft-Gault-derived creatinine clearance (CrCl, ml/min). RESULTS Mean GFR/CrCl was comparable between the groups at LVAD implantation, in the post-implantation period, and at transplantation. Both groups had a significant increase in mean GFR at Week 1 post-implantation (continuous, 59.4 +/- 22.8 to 76.4 +/- 38.6, p = 0.001; pulsatile, 52.5 +/- 21.1 to 69.2 +/- 34.7; p = 0.007), Week 4 (continuous, 59.9 +/- 23.0 to 84.3 +/- 32.9; p < 0.001; pulsatile, 50.3 +/- 21.1 to 79.9 +/- 38.7, p = 0.007), and Week 12 (continuous, 60.3 +/- 23.1 to 75.3 +/- 30.2, p = 0.004; pulsatile, 55.5 +/- 23.1 to 74.2 +/- 27.2, p = 0.037) that was also seen with the Cockcroft-Gault-calculated CrCl. No significant increase occurred in mean GFR/CrCl to transplantation. Incidence of post-implantation renal failure was comparable between the groups (continuous, 38.1%; pulsatile, 31.0%; p = 0.512). CONCLUSIONS After LVAD implantation, patients with continuous flow devices and patients with pulsatile flow devices have comparable renal function.

Inhaled Nitric Oxide Reduces Pulmonary Vascular Resistance More Than Prostaglandin E1 During Heart Transplantation

Heart transplantation in patients with increased pulmonary vascular resistance is often associated with postbypass right heart failure. We therefore compared the abilities of prostaglandin E1 (PGE1) and inhaled nitric oxide to reduce pulmonary vascular resistance during heart transplantation. Patients undergoing orthotopic heart transplantation for congestive heart failure were randomly assigned to either a PGE1 infusion at a rate of 8 ng · kg· −1min−1 starting 10 min before weaning from cardiopulmonary bypass (CPB) (n = 34) or inhalation of 4 ppm nitric oxide starting just before weaning from CPB (n = 34). Both treatments were increased stepwise, if necessary, and were stopped 6 h postoperatively. Hemodynamic values were recorded after the induction of anesthesia, 10 and 30 min after weaning from CPB, and 1 h and 6 h postoperatively. Immediately after weaning from CPB, pulmonary vascular resistance was nearly halved in the nitric oxide group but reduced by only 10% in the PGE1 group. Pulmonary artery pressure was decreased approximately 30% during nitric oxide inhalation, but only approximately 16% during the PGE1 infusion. Six hours after surgery, pulmonary vascular resistance and pulmonary artery pressure were similar in the two groups. The ratio between pulmonary vascular resistance and systemic vascular resistance was significantly less in the nitric oxide patients at all postbypass times. In contrast, the pulmonary-to-systemic vascular resistance ratio increased approximately 30% in the patients given PGE1. Cardiac output, heart rate, mean arterial pressure, right atrial pressure, and pulmonary wedge pressure did not differ between the groups. Weaning from CPB was successful in all patients assigned to nitric oxide inhalation; in contrast, weaning failed in six patients assigned to PGE1 (P = 0.03). Implications: Nitric oxide inhalation selectively reduces pulmonary vascular resistance and pulmonary artery pressure immediately after heart transplantation which facilitates weaning from cardiopulmonary bypass.

Tissue Heat Content and Distribution during and after Cardiopulmonary Bypass at 31 [degree sign]C and 27 [degree sign]C

Background Afterdrop following cardiopulmonary bypass results from redistribution of body heat to inadequately warmed peripheral tissues. However, the distribution of heat between the thermal compartments and the extent to which core‐to‐peripheral redistribution contributes to post‐bypass hypothermia remains unknown. Methods Patients were cooled during cardiopulmonary bypass to nasopharyngeal temperatures near 31 [degree sign]C (n = 8) or 27 [degree sign]C (n = 8) and subsequently rewarmed by the bypass heat exchanger to [almost equal to] 37.5 [degree sign]C. A nasopharyngeal probe evaluated core (trunk and head) temperature and heat content. Peripheral compartment (arm and leg) temperature and heat content were estimated using fourth‐order regressions and integration over volume from 19 intramuscular needle thermocouples, 10 skin temperatures, and “deep” foot temperature. Results In the 31 [degree sign]C group, the average peripheral tissue temperature decreased to 31.9 +/‐ 1.4 [degree sign]C (means +/‐ SD) and subsequently increased to 34 +/‐ 1.4 [degree sign]C at the end of bypass. The core‐to‐peripheral tissue temperature gradient was 3.5 +/‐ 1.8 [degree sign]C at the end of rewarming, and the afterdrop was 1.5 +/‐ 0.4 [degree sign]C. Total body heat content decreased 231 +/‐ 93 kcal. During pump rewarming, the peripheral heat content increased to 7 +/‐ 27 kcal below precooling values, whereas the core heat content increased to 94 +/‐ 33 kcal above precooling values. Body heat content at the end of rewarming was thus 87 +/‐ 42 kcal more than at the onset of cooling. In the 27 [degree sign]C group, the average peripheral tissue temperature decreased to a minimum of 29.8 +/‐ 1.7 [degree sign]C and subsequently increased to 32.8 +/‐ 2.1 [degree sign]C at the end of bypass. The core‐to‐peripheral tissue temperature gradient was 4.6 +/‐ 1.9 [degree sign]C at the end of rewarming, and the afterdrop was 2.3 +/‐ 0.9 [degree sign]C. Total body heat content decreased 419 +/‐ 49 kcal. During pump rewarming, core heat content increased to 66 +/‐ 23 kcal above precooling values, whereas peripheral heat content remained 70 +/‐ 42 kcal below precooling values. Body heat content at the end of rewarming was thus 4 +/‐ 52 kcal less than at the onset of cooling. Conclusions Peripheral tissues failed to fully rewarm by the end of bypass in the patients in the 27 [degree sign]C group, and the afterdrop was 2.3 +/‐ 0.9 [degree sign]C. Peripheral tissues rewarmed better in the patients in the 31 [degree sign]C group, and the afterdrop was only 1.5 +/‐ 0.4 [degree sign]C.

Resistive heating is more effective than metallic-foil insulation in an experimental model of accidental hypothermia: A randomized controlled trial

STUDY OBJECTIVE We study a resistive-heating blanket in a volunteer model of severe accidental hypothermia to evaluate differences in rates of rewarming, core temperature afterdrop, and body heat content and distribution during active and passive rewarming. METHODS Eight volunteers participated in a crossover design on 2 days. The volunteers were anesthetized and cooled to 33 degrees C (91.4 degrees F); anesthesia was subsequently discontinued, and shivering was prevented with meperidine. On one randomly assigned day, the volunteers were rewarmed passively with reflective foil (passive insulation), whereas on the other they were covered with a carbon fiber-resistive heating blanket set to 42 degrees C (107.6 degrees F; active rewarming). Trunk and head temperature and heat content were calculated from core (tympanic membrane) temperature. Peripheral (arm and leg) tissue temperature and heat content were estimated by using fourth-order regressions and integration over volume from 30 tissue and skin temperatures. RESULTS Core heat content increased 73+/-14 kcal (mean+/-SD) during 3 hours of active warming, but only 31+/-24 kcal with passive insulation, a difference of 41+/-20 kcal (95% confidence interval [CI] 27 to 55 kcal; P <. 001). Peripheral tissue heat content increased linearly by 111+/-16 kcal during active warming but only by 38+/-31 kcal during passive warming, a difference of 74+/-34 kcal (95% CI 50 to 97; P <.001). Consequently, total body heat increased 183+/-22 kcal during active warming but only 68+/-54 kcal with passive insulation, a difference of 115+/-42 kcal (95% CI 86 to 144 kcal; P <.001). Core temperature increased from 32.9 degrees C+/-0.2 degrees C to 35.2 degrees C+/-0. 4 degrees C during 3 hours of active warming, a difference of 2.3 degrees C+/-0.4 degrees C. In contrast, core temperature with foil insulation only increased from 32.9 degrees C+/-0.2 degrees C to 33. 8 degrees C+/-0.5 degrees C, a difference of only 0.8 degrees C+/-0. 4 degrees C. The difference in the core temperature increase between the two treatments was thus 1.5 degrees C+/-0.4 degrees C (95% CI 1. 2 degrees C to 1.7 degrees C; P <.001 between treatments). Active warming was not associated with an afterdrop, whereas the afterdrop was 0.2 degrees C+/-0.2 degrees C and lasted a median of 45 minutes (interquartile range, 41 to 64 minutes) with passive insulation. CONCLUSION Resistive heating more than doubles the rewarming rate compared with that produced by reflective metal foil and does so without producing an afterdrop. It is therefore likely to be useful in the prehospital setting.

Relative contribution of skin and core temperatures to vasoconstriction and shivering thresholds during isoflurane anesthesia.

BACKGROUND Thermoregulatory control is based on both skin and core temperatures. Skin temperature contributes approximately 20% to control of vasoconstriction and shivering in unanesthetized humans. However, this value has been used to arithmetically compensate for the cutaneous contribution to thermoregulatory control during anesthesia--although there was little basis for assuming that the relation was unchanged by anesthesia. It even remains unknown whether the relation between skin and core temperatures remains linear during anesthesia. We therefore tested the hypothesis that mean skin temperature contributes approximately 20% to control of vasoconstriction and shivering, and that the contribution is linear during general anesthesia. METHODS Eight healthy male volunteers each participated on 3 separate days. On each day, they were anesthetized with 0.6 minimum alveolar concentrations of isoflurane. They then were assigned in random order to a mean skin temperature of 29, 31.5, or 34 degrees C. Their cores were subsequently cooled by central-venous administration of fluid at approximately 3 degrees C until vasoconstriction and shivering were detected. The relation between skin and core temperatures at the threshold for each response in each volunteer was determined by linear regression. The proportionality constant was then determined from the slope of this regression. These values were compared with those reported previously in similar but unanesthetized subjects. RESULTS There was a linear relation between mean skin and core temperatures at the vasoconstriction and shivering thresholds in each volunteer: r2 = 0.98+/-0.02 for vasoconstriction, and 0.96+/-0.04 for shivering. The cutaneous contribution to thermoregulatory control, however, differed among the volunteers and was not necessarily the same for vasoconstriction and shivering in individual subjects. Overall, skin temperature contributed 21+/-8% to vasoconstriction, and 18+/-10% to shivering. These values did not differ significantly from those identified previously in unanesthetized volunteers: 20+/-6% and 19+/-8%, respectively. CONCLUSIONS The results in anesthetized volunteers were virtually identical to those reported previously in unanesthetized subjects. In both cases, the cutaneous contribution to control of vasoconstriction and shivering was linear and near 20%. These data indicate that a proportionality constant of approximately 20% can be used to compensate for experimentally induced skin-temperature manipulations in anesthetized as well as unanesthetized subjects.

Viennese approach to minimize the invasiveness of ventricular assist device implantation

OBJECTIVE Avoiding full sternotomy and cardiopulmonary bypass (CPB) could significantly reduce the invasiveness of left ventricular assist device (LVAD) implantation. Therefore, we developed minimally invasive implant strategies for the Heartware® VAD (HVAD) and the Thoratec® HeartMate II (HMII) covering isolated LVAD implantation as well as concomitant valve procedures (aortic/tricuspid). We present the surgical techniques and the initial clinical experience. METHODS From February 2012 to March 2013, 27 patients (mean age 58 ± 8 years; male 85%; Ischemic Cardiomyopathy 63%; redo surgery 22%; Interagency Registry for Mechanically Assisted Circulatory Support Level I: 29%, II: 22%, III: 33%, IV-VII: 16%) underwent minimally invasive LVAD implantation at our department. Apical cannulation was performed via a left lateral minithoracotomy in HVAD patients (n = 20) or a left subcostal incision in HMII patients (n = 7). The outflow graft anastomosis was performed to the ascending aorta via a right minithoracotomy in the second intercostal space (n = 22) or the right subclavian artery (n = 2). If additional valve procedures (aortic/tricuspid) were necessary (n = 3), a hemisternotomy was performed to access the valve and perform the outflow graft anastomosis. Circulatory support for LVAD implantation was CPB (33%), extracorporeal membrane oxygenation (48%) or off-pump (19%). RESULTS The minimally invasive approach was feasible in all patients with no need for conversions. Thirty-day and in-hospital mortality were 7.4 and 14.8%, respectively. In-hospital stay was 30.0 ± 22.5 days. One patient (4%) died during follow-up from pump thrombus formation. Three patients (11%) underwent surgical revision for bleeding. CONCLUSIONS Minimally invasive LVAD implantation is feasible and safe. The very encouraging results obtained in this initial series justify a broad application of this technique.

Blood pressure response to thermoregulatory vasoconstriction during isoflurane and desflurane anesthesia

Background:  Mild perioperative hypothermia produces morbid cardiac outcomes that may result from sympathetically induced hypertension. However, volatile anesthetics produce vasodilatation that may reduce the hemodynamic response to hypothermia. We tested the hypothesis that the volatile anesthetics isoflurane and desflurane blunt the normal cold‐induced hypertensive response.